Hey Gary, I'm jealous of your 10 min commute. I have been visiting these refuges yearly since my college biology class field trip in 1962. It is a two hour drive for me and I generally leave early enough to be at the Colusa refuge at dawn. I drive the auto loop at least twice, slowly and with frequent stops. I then drive to Gray Lodge and drive and walk a trail or two. I spend the rest of the day at the Willows refuge. I overnight in Willows and I am at the refuge at dawn on the second day. The mornings are always the most productive for me and, of course have the best light. This time of the year every tree is worth a close look, especially along Logan Creek. The long row of Eucalyptus trees near the end of the auto loop often has an eagle or two and this dead snag on the long west bound part of the loop is a regular stop for one or even two eagles. Getting to know the secrets of these places is a necessary and enjoyable part of the process. I wish you all the best, have fun.
Phil

UPDATE: after talking with Tamron they felt there might be an issue with the lens. Since I also have the 150-600 G2 (and a nicely behaving 90mm macro) I am seriously thinking of sending the 18-400 as well as the 150-600 G2 away for servicing along with my camera body (Canon 7D M2). This is the only body I would use with those two lenses anyhow so...in for a penny, in for a pound. I think the entire kittenkaboodle is headed off to Long Island. Next big trip is end of March, nothing going on in my neck of the woods anyhow.